--- a/testing/mochitest/browser-test.js
+++ b/testing/mochitest/browser-test.js
@@ -418,16 +418,17 @@ function Tester(aTests, structuredLogger
 
   this.MemoryStats = simpleTestScope.MemoryStats;
   this.ContentTask = ChromeUtils.import("resource://testing-common/ContentTask.jsm", null).ContentTask;
   this.BrowserTestUtils = ChromeUtils.import("resource://testing-common/BrowserTestUtils.jsm", null).BrowserTestUtils;
   this.TestUtils = ChromeUtils.import("resource://testing-common/TestUtils.jsm", null).TestUtils;
   this.Promise = ChromeUtils.import("resource://gre/modules/Promise.jsm", null).Promise;
   this.PromiseTestUtils = ChromeUtils.import("resource://testing-common/PromiseTestUtils.jsm", null).PromiseTestUtils;
   this.Assert = ChromeUtils.import("resource://testing-common/Assert.jsm", null).Assert;
+  this.PerTestCoverageUtils = ChromeUtils.import("resource://testing-common/PerTestCoverageUtils.jsm", null).PerTestCoverageUtils;
 
   this.PromiseTestUtils.init();
 
   this.SimpleTestOriginal = {};
   SIMPLETEST_OVERRIDES.forEach(m => {
     this.SimpleTestOriginal[m] = this.SimpleTest[m];
   });
 
@@ -496,16 +497,18 @@ Tester.prototype = {
 
     if (gConfig.jscovDirPrefix) {
       let coveragePath = gConfig.jscovDirPrefix;
       let {CoverageCollector} = ChromeUtils.import("resource://testing-common/CoverageUtils.jsm",
                                                    {});
       this._coverageCollector = new CoverageCollector(coveragePath);
     }
 
+    this.PerTestCoverageUtils.beforeTestSync();
+
     this.structuredLogger.info("*** Start BrowserChrome Test Results ***");
     Services.console.registerListener(this);
     this._globalProperties = Object.keys(window);
     this._globalPropertyWhitelist = [
       "navigator", "constructor", "top",
       "Application",
       "__SS_tabsToRestore", "__SSi",
       "webConsoleCommandController",
@@ -685,16 +688,18 @@ Tester.prototype = {
   },
 
   async nextTest() {
     if (this.currentTest) {
       if (this._coverageCollector) {
         this._coverageCollector.recordTestCoverage(this.currentTest.path);
       }
 
+      this.PerTestCoverageUtils.afterTestSync();
+
       // Run cleanup functions for the current test before moving on to the
       // next one.
       let testScope = this.currentTest.scope;
       while (testScope.__cleanupFunctions.length > 0) {
         let func = testScope.__cleanupFunctions.shift();
         try {
           let result = await func.apply(testScope);
           if (isGenerator(result)) {

--- a/testing/mochitest/tests/SimpleTest/TestRunner.js
+++ b/testing/mochitest/tests/SimpleTest/TestRunner.js
@@ -360,16 +360,20 @@ TestRunner.runTests = function (/*url...
     SpecialPowers.registerProcessCrashObservers();
 
     // Initialize code coverage
     if (TestRunner.jscovDirPrefix != "") {
         var CoverageCollector = SpecialPowers.Cu.import("resource://testing-common/CoverageUtils.jsm", {}).CoverageCollector;
         coverageCollector = new CoverageCollector(TestRunner.jscovDirPrefix);
     }
 
+    let reset = false;
+    SpecialPowers.requestResetCoverageCounters(() => reset = true);
+    SpecialPowers.Services.tm.spinEventLoopUntil(() => reset);
+
     TestRunner._urls = flattenArguments(arguments);
 
     var singleTestRun = this._urls.length <= 1 && TestRunner.repeat <= 1;
     TestRunner.showTestReport = singleTestRun;
     var frame = $('testframe');
     frame.src = "";
     if (singleTestRun) {
         // Can't use document.body because this runs in a XUL doc as well...
@@ -524,16 +528,20 @@ TestRunner.testFinished = function(tests
         TestRunner.updateUI([{ result: false }]);
         return;
     }
 
     if (TestRunner.jscovDirPrefix != "") {
         coverageCollector.recordTestCoverage(TestRunner.currentTestURL);
     }
 
+    let dumped = false;
+    SpecialPowers.requestDumpCoverageCounters(() => dumped = true);
+    SpecialPowers.Services.tm.spinEventLoopUntil(() => dumped);
+
     TestRunner._lastTestFinished = TestRunner._currentTest;
     TestRunner._loopIsRestarting = false;
 
     // TODO : replace this by a function that returns the mem data as an object
     // that's dumped later with the test_end message
     MemoryStats.dump(TestRunner._currentTest,
                      TestRunner.currentTestURL,
                      TestRunner.dumpOutputDirectory,

--- a/testing/mozharness/scripts/desktop_unittest.py
+++ b/testing/mozharness/scripts/desktop_unittest.py
@@ -886,19 +886,21 @@ class DesktopUnittest(TestingMixin, Merc
 
                         executed_tests = executed_tests + 1
 
                     final_cmd = copy.copy(cmd)
                     final_cmd.extend(per_test_args)
 
                     if self.per_test_coverage:
                         gcov_dir, jsvm_dir = self.set_coverage_env(env)
-                        # Per-test reset/dump is only supported for xpcshell and
+                        # Per-test reset/dump is only supported for xpcshell/mochitest and
                         # Linux for the time being.
-                        if not is_baseline_test and suite == 'xpcshell' and self._is_linux():
+                        if not is_baseline_test and \
+                           suite_category in ['mochitest', 'xpcshell'] and \
+                           self._is_linux():
                             env['GCOV_RESULTS_DIR'] = tempfile.mkdtemp()
 
                     return_code = self.run_command(final_cmd, cwd=dirs['abs_work_dir'],
                                                    output_timeout=cmd_timeout,
                                                    output_parser=parser,
                                                    env=env)
 
                     if self.per_test_coverage: